1. Field of the Invention
The present invention relates to a magnetic head device for reading, recording, or erasing signals on a magnetic tape and, more particularly, to a magnetic head device for use in a helical scanning type videotape recorder.
2. Description of the Prior Art
Positioning of a magnetic head is an important factor which determines the quality of the information written on a magnetic tape. Especially, when a plurality of magnetic heads are used for recording, each of the magnetic heads should be located at a determined position so as not to adversely influence each other.
For example, in an video cassette recorder (VCR) of a video home system (VHS), each one of two magnetic heads is located in a symmetric position with respect to the axis of the rotary cylinder and on the same plane perpendicular to the axis. The videotape is wound around a half surface of the rotary cylinder with an inclination angle of approximately 6.degree. with respect to the diametrical circle thereof. Thus, the direction in which the videotape runs is changed along the rotary cylinder such that the wound videotape exhibits a U-shape when viewed from the top of the rotary cylinder. As each of magnetic heads runs over the surface of videotape alternatively, the recorded magnetism pattern is formed on the videotape surface subsequently. The writing pitch between each track in which the magnetism pattern is recorded is a predetermined 60 .mu.m or 20 .mu.m.
It is to be noted that both the magnetic heads should be located on the same plane perpendicular to the axis of the rotary cylinder. If any one of the magnetic heads deviates from the plane by some amount, the preceding magnetism pattern is overwritten by the following magnetism pattern, or a large gap is formed between tracks. In both cases, the recorded magnetism pattern is unevenly formed on the videotape, resulting in a degradation of the signals reproduced from the recorded magnetism pattern.
There two methods are available in the field of this art. A first method involves elastic deformation in the magnetic heads are moved toward an aimed position elastically by pressing a portion of the magnetic head with the means of a screw. The second method involves, as disclosed in U.S. Pat. Ser. No. 07/798,601 filed on Nov. 26, 1991, melting deformation in which a portion of the magnetic head is melted by impinging a laser beam thereon to deform the magnetic head permanently toward the desired position.
In the first method, i.e. elastic deformation with a screw, since the magnetic head is elastically deformed and is temporarily positioned, the magnetic head experiences movement of some .mu.m and can return to the original position due to loosening of the screw, external vibrations, and other causes. Thus, this method can not be applied to the positioning of the magnetic head in which the magnetic patterns are to be recorded, at a writing pitch of 20 .mu.m or smaller.
In the second method, i.e. melting deformation with a laser beam, the magnetic head is deformed permanently and is self-positioned. Thus, this method enables the positioning of the magnetic head with a high accuracy and fine adjustment, and is a very effective means in the field of high density recording. However, it is very difficult to stably control the position of the magnetic head applied with the melting deformation.
Furthermore, since the plate applied with the melting deformation deforms in proportion to the amount of applied heat and in inverse proportion to the plate thickness generally, a longer distance between the melting deformation and the magnetic head gap is required to adjust the position of the magnetic head within a wide range. However, such a magnetic head is supported at one end like a cantilever, so that the head tip at the free end of the magnetic head spaced far from the supported end is easily subjected vibrations caused by the rotating rotary cylinder to prevent the formation of a magnetism pattern on the correct tracks.
Furthermore, if the magnetic head is bent with a larger angle at a portion near the head chip, the head unevenly contacts with the videotape, resulting in a reduction of the reproduced signal output therefrom. Since the portion on which the laser beam is impinged is not specified, the melting deformation methods using the laser beam can not be applied in the mass production of the magnetic heads.